1. Field of the Invention
The present invention relates to a device for temporary storage of flat objects, particularly for a postal sorting machine.
2. The Prior Art
In machines for postal sorting of flat objects, it is frequently necessary to temporarily and individually store the flat objects between an upstream part and a downstream part of the machine.
In a number of cases, it is necessary for the displacement of the flat objects in the temporary storage device to be synchronized between the entry and the exit. Each flat object originating from an upstream conveyor thus experiences a constant delay before being delivered to a downstream conveyor. The operation of such a device is thus of the delay line type.
Such a device is, in particular, described in Patent Application FR-A-2,677,626 and in European Patent Application EP-A-0,480,822.
According to Patent Application FR-A-2,677,626, the temporary storage device includes a rotary drum equipped at its periphery with several longitudinal grooves and arranged in the extension of an entry conveyor on which the flat objects travel one by one in a given direction in a plane which is slightly inclined with respect to the vertical. When a flat object leaves the entry conveyor, its longitudinal lower edge is received in one of the grooves of the drum and its rear face bears against one of the blades of a reception conveyor moved synchronously with the drum. When the drum rotates through a quarter turn, the flat object is maintained parallel to itself by matched advance of the reception conveyor and its lower edge is presented in a pinching zone between a ridge of the drum and a motorized roller which injects the object into the container of an exit conveyor located underneath. During this injection phase, the next groove of the drum is presented in the extension of the entry conveyor in order, there, to receive a further flat object bearing against another blade of the reception conveyor.
Such a device is suited to an operation of the delay line type, but it is not adapted to operation as a stacker/destacker, that is to say when the displacement of the flat objects between the entry and the exit of the device is not synchronized.
EP-A-0,480,822 also describes a temporary storage device of the delay line type using two motorized helical spirals which receive the flat objects traveling in a given direction in an entry conveyor one by one, displace them synchronously, one by one, in a direction orthogonal to their direction in the entry conveyor, and deliver them to an exit station where they are ejected individually into the containers of an exit conveyor located under the helical spiral device.
Such a device is difficult to produce in technical terms, particularly owing to the overhanging assembly of the helical spirals and the need to provide, between the entry conveyor and the helical spirals, orientable arms with drive belts which are capable of directing the flat objects one by one towards a suitable position along helical spirals. Moreover, as in the case of Patent Application FR-A-2,677,626, the device described in this document EP-A-0,480,822 can operate only in delay line mode.
U.S. Pat. No. 3,519,145 describes a temporary storage device consisting of two superposed wheels including radial fins which are uniformly distributed and define, in pairs, compartments capable of receiving flat objects. The two coaxial and superposed wheels are separated by a disk equipped with a slot and a second disk also equipped with a slot is provided under the lower wheel. The two wheels and the intermediate disk are motorized, while the lower disk is stationary. During rotation of the upper wheel, the radial compartments move along in front of an entry conveyor from which they receive letters one by one. By means of an appropriate control of the rotation of the wheels and of the intermediate disk, letters originating from the entry conveyor may be transferred from the upper wheel to the lower wheel through the slot in the intermediate disk, and from the lower wheel towards an exit conveyor through the slot in the stationary lower disk.
Such a device operates in stacker/destacker mode, that is to say the upper wheel receives the letters at the rate of the entry conveyor and that the lower wheel delivers them at the rate of the exit conveyor. The device thus acts as a buffer in which flat objects can remain for variable periods if the entry rate and the exit rate are not synchronized.
Of course, by means of a suitable control of the movement of the two wheels and of the intermediate disk, such a device can also operate in delay line mode if the entry rate and the exit rate have to be synchronized.
However, owing to its design, the device in document U.S. Pat. No. 3,519,145 presents a number of limitations. Thus, its storage capacity is a function of the number of compartments included by the wheels, which compartments have to be sufficiently narrow in order to maintain the letters in a substantially vertical position while having an entry opening of sufficient width to ensure the introduction of the letters originating from the entry conveyor one by one. The increase in the storage capacity thus results in an increase in the diameter of the wheels and a decrease in the angle at the center formed between the walls of a compartment, but this increase rapidly leads to a considerable overall size for the device. The increase in the diameter of the wheels is also reflected in an increase in weight which is liable to pose problems of inertia for the step-by-step driving of the upper wheel in synchronization with the entry conveyor and of the lower wheel in synchronization with the exit conveyor. Moreover, the cylindrical configuration of this temporary storage device offers no possibility of modulation as a function of the space available between entry conveyor and exit conveyor, which can vary from one machine to another. Finally, the letters have to be discharged towards the exit conveyor without the possibility of being directed towards another direction, for example in the event of address non-recognition.
The invention aims to provide a temporary storage device which, according to the particular embodiment given thereto, can operate in delay line mode or in stacker/destacker mode and the configuration of which can easily be adapted as a function of the space available for its installation.
A further object of the invention is to provide such a device which, without damage, makes it possible to transfer individually, at a high rate and in a sure manner, flat objects from an entry conveyor, on which the objects move along in the same plane in a given direction, towards an exit conveyor.
A further object of the invention is to supply such a storage device which has a simple design and is inexpensive, while offering great operational reliability at a high rate for objects with weights and dimensions which can vary within wide margins.